Process for simultaneously preparing 6-aminocapronitrile and hexamethylene diamine

ABSTRACT

A process for coproduction of 6-aminocapronitrile and hexamethylenediamine starting from adiponitrile comprises 
     (1) partially hydrogenating adiponitrile in the presence of a catalyst to obtain a mixture comprising 6-aminocapronitrile, hexamethylenediamine and adiponitrile, 
     (2) removing 6-aminocapronitrile and hexamethylenediamine from the mixture, 
     (3) adding to the portion comprising essentially adiponitrile from 0.01 to 10% by weight of an acid, based on adiponitrile, or an acidic ion exchanger and removing the adiponitrile from the mixture, and 
     (4) recycling the adiponitrile into step (1).

This Application is a 371 of PCT/EP97/04544 filed Aug. 21, 1997.

DESCRIPTION

The present invention relates to a process for coproduction of6-aminocapronitrile and hexamethylenediamine starting from adiponitrileby partial conversion and recovery of unconverted adiponitrile.

DE-A 19 500 222 and German Application 19 548 289.1 disclose a processfor coproduction of 6-aminocapronitrile and hexamethylenediamine byhydrogenation of adiponitrile in the presence of a catalyst with partialconversion, the removal of hexamethylenediamine and 6-aminocapronitrilefrom the mixture and conversion of 6-aminocapronitrile into caprolactamand also recycling into the process of a portion consisting essentiallyof adiponitrile. The disadvantage of this process is that the recycledstream consisting essentially of adiponitrile comprises by-products ofadiponitrile hydrogenation, especially amines such as1-amino-2-cyanocyclopentene (ACCPE),2-(5-cyanopentylamino)tetrahydroazepine (CPATRA) andbishexamethylenetriamine (BHMTA).

The by-products cannot be removed from adiponitrile by distillation inthe processes described because of the formation of azeotropes orquasi-azeotropes, but build up in the process as a result of therecycling. ACCPE recycled into the hydrogenation forms2-aminomethylcyclopentylamine (AMCPA), which contaminates thehexamethylenediamine product. It is known from U.S. Pat. No. 3,696,153that AMCPA is very difficult to separate from hexamethylenediamine.

It is an object of the present invention to provide a process forcoproduction of 6-aminocapronitrile and hexamethylenediamine fromadiponitrile by partial conversion and recovery of unconvertedadiponitrile without the disadvantages mentioned and whereby theunconverted adiponitrile is technically simple and economical toseparate off and purify.

We have found that this object is achieved by a process for coproductionof 6-aminocapronitrile and hexamethylenediamine starting fromadiponitrile, which comprises

(1) partially hydrogenating adiponitrile in the presence of a catalystto obtain a mixture comprising 6-aminocapronitrile, hexamethylenediamineand adiponitrile,

(2) removing 6-aminocapronitrile and hexamethylenediamine from themixture,

(3) adding to the portion comprising essentially adiponitrile from 0.01to 10% by weight of an acid, based on adiponitrile, or an acidic ionexchanger and removing the adiponitrile from the mixture, and

(4) recycling the adiponitrile into step (1).

The partial hydrogenation of adiponitrile can be carried out by one ofthe known processes, for example by one of the abovementioned processesdescribed in U.S. Pat. No. 4,601,859, U.S. Pat. No. 2,762,835, U.S. Pat.No. 2,208,598, DE-A 848 654, DE-A 954 416, DE-A 4 235 466 or WO92/21650, by effecting the hydrogenation in general in the presence ofnickel-, cobalt-, iron- or rhodium-containing catalysts. The catalystsmay be used in the form of supported catalysts or unsupported catalysts.Examples of suitable catalyst carriers are alumina, silica, titaniumdioxide, magnesium oxide, active carbons and spinels. Examples ofsuitable unsupported catalysts are Raney nickel and Raney cobalt.

The catalyst space velocity is usually chosen in the range from 0.05 to10, preferably from 0.1 to 5, kg of adiponitrile per 1 of catalyst perhour.

Hydrogenation is carried out, as a rule, at from 20 to 200° C.,preferably from 50 to 150° C., and at hydrogen partial pressures of from0.1 to 40, preferably from 0.5 to 30, MPa.

The hydrogenation is preferably carried out in the presence of asolvent, in particular ammonia. The amount of ammonia is chosen ingeneral in the range from 0.1 to 10, preferably from 0.5 to 3, kg ofammonia per kg of adiponitrile.

The molar ratio of 6-aminocapronitrile to hexamethylenediamine and hencethe molar ratio of caprolactam to hexamethylenediamine can be controlledby the adiponitrile conversion chosen in each case. Adiponitrileconversions of from 10 to 90%, preferably from 30 to 80%, are preferablyemployed in order to obtain high 6-aminocapronitrile selectivities.

As a rule, the sum total of 6-aminocapronitrile and hexamethylenediamineis from 95 to 99%, depending on the catalyst and reaction conditions,hexamethyleneimine being the most important by-product in terms ofquantity.

In a preferred embodiment, the reaction is carried out in the presenceof ammonia and lithium hydroxide or a lithium compound which formslithium hydroxide under the reaction conditions, at from 40 to 120° C.,preferably from 50 to 100° C., particularly preferably from 60 to 90°C.; the pressure is chosen in general in the range from 2 to 12,preferably from 3 to 10, particularly preferably from 4 to 8, MPa. Theresidence times are essentially dependent on the desired yield, theselectivity and the desired conversion; usually, the residence time ischosen so that a maximum yield is achieved, for example in the rangefrom 50 to 275, preferably from 70 to 200, minutes.

The pressure and temperature ranges are preferably chosen so that thereaction can be carried out in the liquid phase.

Ammonia is used in general in an amount such that the weight ratio ofammonia to dinitrile is from 9:1 to 0.1:1, preferably from 2.3:1 to0.25:1, particularly preferably from 1.5:1 to 0.4:1.

The amount of lithium hydroxide is chosen as a rule in the range from0.1 to 20, preferably from 1 to 10, % by weight, based on the amount ofcatalyst used.

Examples of lithium compounds which form lithium hydroxide under thereaction conditions are lithium metal and alkyllithium and aryllithiumcompounds such as n-butyllithium and phenyllithium. The amount of thesecompounds is chosen in general so that the abovementioned amount oflithium hydroxide is obtained.

Preferred catalysts are nickel-, ruthenium-, rhodium-, iron- andcobalt-containing compounds, preferably those of the Raney type, inparticular Raney nickel and Raney cobalt. The catalysts may also be usedin the form of supported catalysts, carriers which may be used being,for example, alumina, silica, zinc oxide, active carbon and titaniumdioxide (cf. Appl. Het. Cat. (1987), 106-122; Catalysis 4 (1981), 1-30).Raney nickel (for example from BASF AG, Degussa and Grace) isparticularly preferred.

The nickel, ruthenium, rhodium, iron and cobalt catalysts may bemodified with metals of groups VIB (Cr, Mo, W) and VIII (Fe, Ru, Os, Co(only in the case of nickel), Rh, Ir, Pd, Pt) of the Periodic Table.Observations to date have shown that the use of, in particular, modifiedRaney nickel catalysts, for example modified with chromium and/or iron,leads to higher aminonitrile selectivities (for preparation, cf. DE-A 2260 978 and Bull. Soc. Chem. 13 (1946), 208).

The amount of catalyst is chosen in general so that the amount ofcobalt, ruthenium, rhodium, iron or nickel is from 1 to 50, preferablyfrom 5 to 20, % by weight, based on the amount of dinitrile used.

The catalysts may be used as fixed-bed catalysts by the liquid phase ortrickle-bed procedure or as suspended catalysts.

In a further preferred embodiment, adiponitrile is partiallyhydrogenated to 6-aminocapronitrile at elevated temperatures and highpressure in the presence of a solvent and of a catalyst which comprises

(a) a compound based on a metal selected from the group consisting ofnickel, cobalt, iron, ruthenium and rhodium,

(b) from 0.01 to 25, preferably from 0.1 to 5, % by weight, based on(a), of a promoter based on a metal selected from the group consistingof palladium, platinum, iridium, osmium, copper, silver, gold, chromium,molybdenum, tungsten, manganese, rhenium, zinc, cadmium, lead, aluminum,tin, phosphorus, arsenic, antimony, bismuth and rare earth metals, and

(c) from 0 to 5, preferably from 0.1 to 3, % by weight, based on (a), ofa compound based on an alkali metal or an alkaline earth metal,

with the proviso that, if a compound based on only ruthenium or rhodiumor ruthenium and rhodium or nickel and rhodium is chosen as component(a), said promoter (b) can, if desired, be dispensed with, and with thefurther proviso that said component (a) shall not be based on iron whensaid component (b) is aluminum.

Preferred catalysts are those in which the component (a) comprises atleast one compound based on a metal selected from the group consistingof nickel, cobalt and iron, in an amount of from 10 to 95% by weight andruthenium and/or rhodium in an amount of from 0.1 to 5% by weight, basedin each case on the sum of components (a) to (c),

component (b) comprises at least one promoter based on a metal selectedfrom the group consisting of silver, copper, manganese, rhenium, leadand phosphorus, in an amount of from 0.1 to 5% by weight, based on (a),and

component (c) comprises at least one compound based on the alkali metalsand alkaline earth metals, selected from the group consisting oflithium, sodium, potassium, cesium, magnesium and calcium, in an amountof from 0.1 to 5% by weight.

Particularly preferred catalysts are:

catalyst A, comprising 90% by weight of cobalt oxide (CoO), 5% by weightof manganese oxide (Mn₂O₃), 3% by weight of phosphorus pentoxide and 2%by weight of sodium oxide (Na₂O),

catalyst B, comprising 20% by weight of cobalt oxide (CoO), 5% by weightof manganese oxide (Mn₂O₃), 0.3% by weight of silver oxide (Ag₂O), 70%by weight of silica (SiO₂), 3.5% by weight of alumina (Al₂O₃), 0.4% byweight of iron oxide (Fe₂O₃), 0.4% by weight of magnesium oxide (MgO)and 0.4% by weight of calcium oxide (CaO), and

catalyst C, comprising 20% by weight of nickel oxide (NiO), 67.42% byweight of silica (SiO₂), 3.7% by weight of alumina (Al₂O₃), 0.8% byweight of iron oxide (Fe₂O₃), 0.76% by weight of magnesium oxide (MgO),1.92% by weight of calcium oxide (CaO), 3.4% by weight of sodium oxide(Na₂O) and 2.0% by weight of potassium oxide (K₂O).

Such catalysts are described for example in DE-A 195 002 22 and GermanApplication 195 482 89.1.

Particularly preferred catalysts are those comprising

a) a compound based on iron such as iron oxide,

b) from 0 to 5% by weight, based on (a), of a promoter based on anelement or 2, 3, 4 or 5 elements selected from the group consisting ofaluminum, silicon, zirconium, vanadium and titanium, and

c) from 0 to 5% by weight, preferably from 0.1 to 3% by weight,especially from 0.1 to 0.5% by weight, based on (a), of a compound basedon an alkali or alkaline earth metal, preferably selected from the groupconsisting of lithium, sodium, potassium, rubidium, cesium, magnesiumand calcium.

The catalysts which may be preferably used may be unsupported catalystsor supported catalysts. Examples of suitable carrier materials areporous oxides, such as alumina, silica, aluminosilicates, lanthanumoxide, titanium dioxide, zirconium dioxide, magnesium oxide, zinc oxideand zeolites, and active carbon or mixtures thereof.

The preparation is carried out as a rule by a procedure in whichprecursors of the components (a) are precipitated together withprecursors of the promoters (components (b)) and, if desired, withprecursors of the trace components (c) in the presence or absence ofcarrier materials (depending on the catalyst type desired), if desiredthe resulting catalyst precursor is processed to give extrudates orpellets and is dried and then calcined. Supported catalysts aregenerally also obtainable by impregnating the carrier with a solution ofthe components (a), (b) and, if desired, (c), it being possible to addthe individual components simultaneously or in succession, or byspraying the components (a), (b) and, if desired, (c) onto the carrierby a method known per se.

Suitable precursors of the components (a) are as a rule readilywater-soluble salts of the abovementioned metals, such as nitrates,chlorides, acetates, formates and sulfates, preferably nitrates.

Suitable precursors of the components (b) are as a rule readilywater-soluble salts or complex salts of the abovementioned metals, suchas nitrates, chlorides, acetates, formates and sulfates and inparticular hexachloroplatinate, preferably nitrates andhexachloroplatinate.

Suitable precursors of the components (c) are as a rule readilywater-soluble salts of the abovementioned alkali metals and alkalineearth metals, such as hydroxides, carbonates, nitrates, chlorides,acetates, formates and sulfates, preferably hydroxides and carbonates.

The precipitation is generally effected from aqueous solutions,alternatively by adding precipitating reagents, by changing the pH or bychanging the temperature.

The catalyst precursor thus obtained is usually dried, generally at from80 to 150° C., preferably from 80 to 120° C.

The calcination is usually carried out at from 150 to 500° C.,preferably from 200 to 450° C., in a gas stream comprising air ornitrogen.

After calcination, the catalyst material obtained is generally exposedto a reducing atmosphere (activation), for example by exposing it forfrom 2 to 24 hours to a hydrogen atmosphere or a gas mixture containinghydrogen and an inert gas, such as nitrogen, at from 80 to 250° C.,preferably from 80 to 180° C., in the case of catalysts based onruthenium or rhodium as component (a) or at from 200 to 500° C.,preferably from 250 to 400° C., in the case of catalysts based on one ofthe metals selected from the group consisting of nickel, cobalt and ironas component (a). The catalyst loading here is preferably 200 l per l ofcatalyst.

Advantageously, the activation of the catalyst is carried out directlyin the synthesis reactor, since this usually dispenses with an otherwisenecessary intermediate step, ie. the passivation of the surface, usuallyat from 20 to 80° C., preferably from 25 to 35° C., by means ofoxygen/nitrogen mixtures, such as air. The activation of passivatedcatalysts is then preferably carried out in the synthesis reactor atfrom 180 to 500° C., preferably from 200 to 350° C., in ahydrogen-containing atmosphere.

The catalysts may be used as fixed-bed catalysts by the liquid phase ortrickle-bed procedure or as suspended catalysts.

If the reaction is carried out in a suspension, temperatures of from 40to 150° C., preferably from 50 to 100° C., particularly preferably from60 to 90° C., are usually chosen; the pressure is chosen in general inthe range from 2 to 30, preferably from 3 to 30, particularly preferablyfrom 4 to 9, MPa. The residence times are essentially dependent on thedesired yield, the selectivity and the desired conversion; usually, theresidence time is chosen so that a maximum yield is achieved, forexample in the range from 50 to 275, preferably from 70 to 200, minutes.

In the suspension procedure, preferably used solvents are ammonia,amines, diamines and triamines of 1 to 6 carbon atoms, such astrimethylamine, triethylamine, tripropylamine and tributylamine, oralcohols, in particular methanol and ethanol, particularly preferablyammonia. A dinitrile concentration of from 10 to 90, preferably from 30to 80, particularly preferably from 40 to 70, % by weight, based on thesum of dinitrile and solvent, is advantageously chosen.

The amount of catalyst is chosen in general in the range from 1 to 50,preferably from 5 to 20, % by weight, based on the amount of dinitrileused.

The suspension hydrogenation may be carried out batchwise or,preferably, continuously, as a rule in the liquid phase.

The partial hydrogenation can also be carried out batchwise orcontinuously in a fixed-bed reactor by the trickle-bed or liquid phaseprocedure, a temperature of from 20 to 150° C., preferably from 30 to90° C., and a pressure of, as a rule, from 2 to 40, preferably from 3 to20, MPa usually being chosen. The partial hydrogenation is preferablycarried out in the presence of a solvent, preferably ammonia, an amine,a diamine or a triamine of 1 to 6 carbon atoms, such as trimethylamine,triethylamine, tripropylamine or tributylamine, or an alcohol,preferably methanol or ethanol, particularly preferably ammonia. In apreferred embodiment, an ammonia content of from 1 to 10, preferablyfrom 2 to 6, g per g of adiponitrile is chosen. A catalyst spacevelocity of from 0.1 to 2.0, preferably from 0.3 to 1.0, kg ofadiponitrile per 1 per h is preferably chosen. Here too, the conversionand hence the selectivity can be controlled by changing the residencetime.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 depicts a flow diagram of the apparatus used to carry out themethod of the present invention.

The partial hydrogenation can be carried out in a conventional reactorsuitable for this purpose (R1 in the drawing).

The hydrogenation affords a mixture comprising 6-aminocapronitrile,hexamethylenediamine and adiponitrile.

The removal from the mixture of 6-aminocapronitrile,hexamethylenediamine and a portion comprising essentially adiponitrilecan be effected in a conventional manner, preferably by distillation,for example as described in DE-A 195 002 22 or German Application 19 548289.1, simultaneously or in succession.

The distillation in the first column (K1 in the drawing) is carried outby a method in which the mixture comprising essentially6-aminocapronitrile, hexamethylenediamine, ammonia, adiponitrile andhexamethyleneimine, preferably a mixture comprising essentially from 1to 70, preferably from 5 to 40, % by weight of 6-aminocapronitrile,

from 1 to 70, preferably from 5 to 40, % by weight of adiponitrile,

from 0.1 to 70, preferably from 1 to 40, % by weight ofhexamethylenediamine,

from 0.01 to 10, preferably from 0.05 to 5, % by weight ofhexamethyleneimine and

from 5 to 95, preferably from 20 to 85, % by weight of ammonia, iscarried out as a rule in a conventional distillation column at a bottomtemperature of from 60 to 250° C., preferably from 100 to 200° C., and apressure of from 5 to 30, preferably from 12 to 25, bar in the presenceof one or more compounds A which are inert under the distillationconditions and boil at from 60 to 220° C. at 18 bar, to give ammonia asthe top product and a bottom product I, the ammonia not being completelyseparated off.

Suitable compounds A are substances which are inert under thedistillation conditions and have a boiling point of from 60 to 250° C.,preferably from 60 to 150° C., at 18 bar. Examples are alkanes,cycloalkanes, aromatics, naphthenes, alcohols, ethers, nitriles andamines having the abovementioned properties, in particular C₅-C₈-alkanesand C₂-C₄-alkanols, particularly preferably n-pentane, cyclohexane,triethylamine, ethanol, acetonitrile, n-hexane, di-n-propyl ether,isopropanol, n-butylamine and benzene, very particularly preferablyethanol.

Compound A is usually added in an amount of from 0.1 to 50, preferablyfrom 1 to 10, % by weight, based on the bottom product I.

The bottom product I, comprising essentially 6-aminocapronitrile,hexamethylenediamine, adiponitrile, hexamethyleneimine, inert compoundor compounds A and ammonia, the ammonia content being lower than that ofthe mixture obtained from the reactor R1, is subjected to a seconddistillation to give a mixture of the inert compound or compounds A andammonia as the top product and a bottom product II, the distillationbeing carried out at a bottom temperature of from 100 to 250° C.,preferably from 140 to 200° C., and at from 2 to 15, preferably from 4to 12, bar, with the proviso that the pressures of the first and of thesecond column (K2 in the drawing) are matched with one another so that atop temperature of more than 20° C. is obtained at a respective bottomtemperature of not more than 250° C. It may also be advantageous tocarry out the condensation at the top of the second column at lowertemperatures, the top product, which consists of pure or relativelyhighly concentrated ammonia, being recycled to the first column, or

to recycle the top product of the second column in vapor form, afterincreasing the pressure by means of a compressor, to the first column orto its condenser.

The bottom product II, comprising essentially 6-aminocapronitrile,hexamethylenediamine, adiponitrile, hexamethyleneimine and inertcompound or compounds A, is subjected to a distillation in a thirdcolumn (K3 in the drawing) to give the inert compound or compounds A asthe top product and a bottom product III, the distillation being carriedout at a bottom temperature of from 50 to 250° C., preferably from 140to 200° C., and at from 0.05 to 2, preferably from 0.2 to 1, bar, withthe proviso that the inert compound or compounds A obtained as the topproduct is or are fed to the second column, and, if desired, thedistillation is carried out in the presence of one or more compounds Bwhich are inert under the distillation conditions and boil at from 20 to250° C., preferably from 60 to 170° C., at a given pressure of 0.3 bar.

Examples of compounds B are alkanes, cycloalkanes, aromatics,naphthenes, alcohols, ethers, nitrites and amines having theabovementioned properties, in particular di-n-butyl ether,valeronitrile, n-octane, cyclooctane, n-hexylamine, hexamethyleneimineand hexamethylenediamine, preferably hexamethyleneimine and/orhexamethylenediamine, particularly preferably hexamethyleneimine.

In a preferred embodiment, hexamethyleneimine and/orhexamethylenediamine are chosen as compound B or, particularlypreferably, no further compound B is added.

Compound B is preferably added to the column K3 in an amount of from0.01 to 50, preferably from 0.5 to 10, % by weight, based on the bottomproduct II.

The bottom product III, comprising essentially 6-aminocapronitrile,hexamethylenediamine, adiponitrile, hexamethyleneimine and, if desired,inert compound or compounds B, is subjected to a distillation in afourth column (K4 in the drawing) to give a top product KP1, containingessentially hexamethyleneimine, if desired inert compound or compounds Band a side stream SA1, comprising essentially hexamethylenediamine, thebottom temperature of the column being from 50 to 250° C. and thepressure from 0.05 to 1.5 bar, and to give a bottom product IV.

If desired, the column is equipped with a dividing wall in the regionbetween feed and side take-off point (Petlyuk column) so that thehexamethylenediamine obtained is essentially free of hexamethyleneimineand inert compound or compounds B and of other low boilers,

top product KP1 and/or HMD from the side stream SA1 being fed, ifrequired, to the third column or, if required, only a part thereof beingfed to the third column and the remainder being removed.

The bottom product IV, comprising essentially 6-aminocapronitrile andadiponitrile and possibly high boilers, is subjected to a distillationin a fifth column (K5 in the drawing) to give 6-aminocapronitrile havinga purity of at least 95%, preferably from 99 to 99.9%, as the topproduct and a side stream V consisting essentially of adiponitrile and abottom product V which consists of high boilers and small amounts ofadiponitrile.

If desired, the column is equipped with a dividing wall in the regionbetween feed and side take-off point, so that the adiponitrile obtainedcomprises relatively small amounts of high boilers, the distillationbeing carried out at a bottom temperature of from 50 to 250° C. and atfrom 10 to 300 mbar.

Instead of obtaining adiponitrile as side stream V, it is also possibleto separate bottom product V from column K5, comprising adiponitrile andhigher boiling compounds, by distillation in a further column K6 toobtain adiponitrile as top product VI.

According to the invention, the portion comprising essentiallyadiponitrile, which in the disclosed distillative workup of theadiponitrile hydrogenation mixture is obtained as side stream V ofcolumn K5, as top product VI of column K6 or as bottom product of columnK5, preferably as side stream V of column K5 [sic], is treated with anacid or an acidic ion exchanger.

Suitable acids or acidic ion exchangers are primarily substances whichcan function as proton donors with respect to primary, secondary andtertiary saturated and unsaturated amines such as enamines. Acids havinga pKa value of at most 10, preferably at most 7, are particularlysuitable.

Suitable acids include inorganic acids such as nitric acid, preferablysulfuric acid, in particular as 100% strength by weight sulfuric acid oras an at least 90% by weight, preferably 96% by weight, mixtureespecially with water or phosphoric acid, organic acids, for examplecarboxylic acids such as adipic acid, 2-ethylhexanoic acid, pimelicacid, suberic acid, undecanedioic acid, terephthalic acid,cyclohexanecarboxylic acid, for example sulfonic acid such asp-toluenesulfonic acid, benzenesulfonic acid, acidic ion exchangers suchas Lewatit S100G1, Amberlyst 15, Dowex 50 WX 8, Bay. Kat. K 2431,Amberlite IR-120, for example, and also mixtures of such acids andacidic ion exchangers.

The reaction of the adiponitrile with the acid can be effected in thepresence of a liquid diluent such as water, in which case the liquiddiluent can be added to the adiponitrile together with the acid orbefore or after the acid.

The direct treatment of adiponitrile which has not been freed fromhigher boiling compounds, for example the bottom product V of column K5,if it does not contain adiponitrile side stream, is likewise possible.In this case, the consumption of acid or acidic ion exchanger and theamount of residue produced after the adiponitrile has been removedincreases.

The molar ratio of acid groups to the basic compounds present in theresidue should be at least equimolar, preferably superequimolar. It hasbeen found to be advantageous to add from 0.01 to 10% by weight, inparticular from 0.1 to 2% by weight, of acid, based on adiponitrile.

The reaction of the adiponitrile with the acid can be effected in aconventional manner, as by mixing or passing the adiponitrile through afixed ion exchanger bed, advantageously at temperatures from 2 to 250°C., especially from 30 to 100° C., the resulting reaction times rangingfrom 1 second to 30 minutes, in particular from 1 second to 10 minutes.

The adiponitrile can be removed from the mixture in a conventionalmanner, advantageously by distillation or extraction.

If a liquid diluent such as water is added during the reaction of theresidue with the acid, the liquid diluent can preferably be removed byadsorption, especially distillation, before the adiponitrile is removed.

Similarly, the reaction products obtained after the acid has been addedand any excess acid can advantageously be removed from adiponitrile byextraction, for example with water.

The adiponitrile obtained by the process of this invention can bere-used for partial hydrogenation to hexamethylenediamine and6-aminocapronitrile without a buildup of by-products which prevent anon-spec production of hexamethylenediamine and/or 6-aminocapronitrileand/or adversely affect the on-stream time of the catalyst for thepartial hydrogenation.

The 6-aminocapronitrile can subsequently be processed in a conventionalmanner, optionally via the intermediate stage of caprolactam, intonylon-6, while hexamethylenediamine can be processed with adipic acidinto nylon-6,6. Nylon-6 and nylon-6,6 are industrially importantmaterials of construction.

Abbreviations: ADN=adiponitrile, ACN=6-aminocapronitrile,HMD=hexamethylenediamine

EXAMPLE 1

a) Preparation of Crude ADN

A tubular reactor 2 m in length and 2.5 cm in internal diameter wascharged with 750 ml (1534 g) of a catalyst consisting of 90% by weightof CoO, 5% by weight of Mn₂O₃, 3% by weight of P₂O₅ and 2% by weight ofNa₂O. The catalyst was subsequently activated over 48 h underatmospheric pressure in a 500 l/h hydrogen stream by raising thetemperature from 30° C. to 280° C. At 70° C. the reactor was supplied at200 bar with a mixture of 400 ml/h adiponitrile, 930 ml/h of ammonia and500 l/h of hydrogen. After 50 hours the conversion was 67% and thereaction mixture consisted essentially of 32% by weight of ADN, 48% byweight of ACN and 19% by weight of HMD. The hydrogenation effluent wascollected for a period of 3000 hours after removal of ammonia.

6-Aminocapronitrile and hexamethylenediamine were removed from thehydrogenation effluent by distillation. Then 2.9 kg/h of adiponitrilewere distilled off overhead in a column having 4 theoretical plates at atop-of-column pressure of 20 mbar, leaving 150 g/h of residue behind atthe base of the column. The adiponitrile comprised 9400 ppm ofbishexamethylenetriamine (BHMTA), 320 ppm of2-(5-cyanopentylamino)tetrahydroazepine (CPATHA) and 280 ppm of1-amino-2-cyanocyclopentene (ACCPE).

b) Purification of Crude ADN

After the distillation, the adiponitrile was admixed in a stirredautoclave with 25 g/h of 96% strength H₂SO₄ and stirred at roomtemperature for 10 minutes. Water was then separated from theadiponitrile at 30 mbar as the overhead product of the column, and theadiponitrile was distilled in a subsequent stage at 10 mbar. 100 g/h ofresidue were left as bottom product. The purified adiponitrile comprisedless than 30 ppm of BHMTA, 10 ppm of ACCPE and 30 ppm of CPATHA and wasrecycled into the partial hydrogenation. Here the conditions of Example1a) resulted in a reactor effluent comprising 34% of ADN, 49% of ACN and16% of HMD at a conversion of 64%.

EXAMPLE 2

ADN (2.7 kg/h) removed from the hydrogenation effluent and distilled offoverhead according to Example 1a) was admixed in a stirred autoclavewith 100 g/h of 25% strength H₃PO₄ and stirred at room temperature for10 minutes. Water was then separated from the adiponitrile at 30 mbar asoverhead product of a column having 10 theoretical plates, and theadiponitrile was distilled in a subsequent stage at 10 mbar. 90 g/h ofresidue were left as bottom product. The purified adiponitrile comprisedless than 30 ppm of BHMTA, 30 ppm of CPATHA and 10 ppm of ACCPE and wasrecycled into the partial hydrogenation. Here no change in the catalystactivity or the ACN/HMD selectivity was found under the conditions ofExample 1a).

EXAMPLE 3

ADN removed from the hydrogenation effluent and distilled off overheadaccording to Example 1a) was passed at room temperature through anacidic ion exchanger (Dowex 50 WX 8). After the ion exchanger, thepurified adiponitrile comprised less than 30 ppm of BHMTA, 30 ppm ofCPATHA and 10 ppm of ACCPE and was recycled into the partialhydrogenation. Here no change in the catalyst activity or the ACN/HMDselectivity was found under the conditions of Example 1a).

We claim:
 1. A process for coproduction of 6-aminocapronitrile andhexa-methylonediamine starting from adiponitrile, which comprises (1)partially hydrogenating adiponitrile in the presence of a catalyst toobtain a mixture comprising 6-aminocapronitrile, hexamethylenediamineand adiponitrile, (2) removing 6-aminocapronitrile andhexamethylenediamine from the mixture, (3) adding to the mixturecomprising adiponitrile from 0.01 to 10% by weight of an acid, based onadiponitrile, or an acidic ion exchanger and removing the adiponitrilefrom the mixture, and (4) recycling the adiponitrile into step (1).
 2. Aprocess as claimed in claim 1, wherein the adiponitrile is removed fromthe mixture in step (3) by distillation or extraction.
 3. A process asclaimed in claim 1, wherein the hydrogenation is carried out in thepresence of a liquid diluent.
 4. A process as claimed in claim 1 in thepresence of a liquid diluent, further comprising removing the liquiddiluent between steps (1) and (2).
 5. A process as claimed in claim 1,wherein the catalyst used comprises (a) a compound based on a metalselected from the group consisting of nickel, cobalt, iron, rutheniumand rhodium, (b) from 0.01 to 25% by weight, based on (a), of a promoterbased on a metal selected from the group consisting of palladium,platinum, iridium, osmium, copper, silver, gold, chromium, molybdenum,tungsten, manganese, rhenium, zinc, cadmium, lead, aluminum, tin,phosphorus, arsenic, antimony, bismuth and rare earth metals, and (c)from 0 to 5% by weight, based on (a), of a compound based on an alkalimetal or an alkaline earth metal, with the proviso that, if a compoundbased on only ruthenium or rhodium or ruthenium and rhodium or nickeland rhodium is chosen as component (a), said promoter (b) can, ifdesired, be dispensed with, and with the further proviso that saidcomponent (a) shall not be based on iron when said component (b) isaluminum.
 6. A process as claimed in claim 1, wherein the catalyst usedcomprises (a) a compound based on iron, (b) from 0 to 5% by weight,based on (a), of a promoter based on an element or 2, 3, 4 or 5 elementsselected from the group consisting of aluminum, silicon, zirconium,vanadium and titanium, and (c) from 0 to 5% by weight, based on (a), ofa compound based on an alkali metal or an alkaline earth metal.
 7. Aprocess as claimed in claim 1, wherein the adiponitrile is removed fromthe mixture by distillation and the acid used has a higher boiling pointthan adiponitrile under the distillation pressure.
 8. A process asclaimed in claim 1, wherein the acid used has a pK_(a) value of at most10.
 9. A process as claimed in claim 1, wherein a portion comprisingadiponitrile is removed between steps (2) and (3).
 10. A process asclaimed in claim 1, wherein the acid used in step (3) is sulfuric acidor a mixture comprising at least 90% by weight of sulfuric acid.
 11. Aprocess as claimed in claim 5, wherein the catalyst used comprises from0.1 to 5% by weight, based on (a), of a promoter based on a metalselected from the group consisting of palladium, platinum, iridium,osmium, copper, silver, gold, chromium, molybdenum, tungsten, maganese,rhenium, zinc, cadmium, lead, aluminum, tin, phosphorus, arsenic,antimony, bismuth and rare earth metals.
 12. A process as claimed inclaim 5, wherein the catalyst used comprises from 0.1 to 3% by weight,based on (a), of a compound based on an alkali metal or an alkalineearth metal.